1. Field of the Invention
This invention relates to line image sensors to be used for reading written materials such as facsimile documents, and to element structures which control photosensitivities of photoelectric transfer elements of which the line image sensors consist either on an inter-element basis or on an element basis.
2. Description of the Related Art
Conventional photoelectric transfer elements are, as disclosed in Japanese Patent Unexamined Publication No. 58-63164. They are of such sandwiched type with a photoconductive film is interposed between a top transparent electrode and a bottom metal electrode. On the other hand, photoelectric transfer elements which receive light along the side of the bottom electrode are discussed in pages 53 to 56 in the proceedings of the Electronic Photography Society Symposium "Where Are We Now with Amorphous Silicon Devices" published in May 1985.
Conventional photoelectric transfer elements are of the so-called sandwiched type in which a photoconductive film is interposed between a bottom electrode and a top transparent electrode. Both electrodes sandwiching the photoconductive film are so arranged that the photoconductive film protrudes out from the bottom electrode in order to prevent both electrodes from being short-circuited by the photoconductive film. For this reason, when performing a so-called direct contact type reading in which written material is irradiated through a substrate by a light source provided at the rear side of the substrate with reflected light received. The light from the light source directly irradiates the photoconductive film which protrudes from the bottom electrode. Thus a photoelectric current is generated, and such photoelectric current becomes noise against photoelectric current generated by the light reflected from the written material irradiating the photoconductive film, thereby causing the reading quality to be impaired, and this has long been a problem. Furthermore, in conventional photoelectric transfer elements, since the photoconductive film continuously covers a plurality of photoelectric transfer elements, a problem has existed in that they are susceptible to so-called "cross talk," or output current variations caused by voltages of neighboring photoelectric transfer elements and the amounts of the irradiated light.